Crucible for vaporizing metal



March 1965 H. R. SMITH, JR 3,172,649

CRUCIBLE FOR VAPORIZING METAL Filed April 1, 1963 I IIIIIIIIIIIIII INVENTOR. HUG/1' E. SMITH JR.

Attorney United states Patent 3,172,649 CRUCEBLE F912 VAPGRIZTNG METAL Hugh R. Smith, In, Piedmont, Calif., assignor, by mesne assignments, to United States teel Corporation Filed Apr. 1, 1963, Ser. No. 269,451 4 Claims. (Cl. 2633-43) This invention relates to a crucible or support for metal, e.g., aluminum, to be vaporized under high-vacuum, high-temperature conditions.

The evaporation of aluminum for coating by vapor condensation presents a serious problem in crucibles because the molten metal from which the vapor boils off is highly reactive with most materials which might be used to support it. My copending application Serial No. 133,089, filed August 22, 1961, discloses and claims a crucible composed of a block of refractory material confined within a Water-cooled jacket, adapted to have its upper surface highly heated by electron bombardment. I have now invented a crucible which is an improvement on that type in the matter of thermal efficiency.

It is the object of my present invention to provide a crucible having a highly effective barrier against the loss of heat from the heated mass of refractory material to the water-cooled support therefor. in a preferred embodiment, I provide a water-cooled supporting shell of metal with a lining of refractory material such as alumina. I further provide an inner lining of refractory metal such as molybdenum, within the alumina lining. The dual lining is preferably duplicated within itself and the inner dual lining contains the mass of refractory metal such as zirconium from which the aluminum is actually vaporized.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the present preferred embodiment. In the draw mgs:

' FIGURE 1 is a plan view;

FIGURE 2 is an elevation with a portion in longitudi nal section along the plane of line IIII of FIGURE 1; and

FIGURE 3 is a cross section taken along the plane of line III-Ill of FIGURE 2.

Referring now in detail to the drawings, my improved crucible comprises a semi-cylindrical receptacle 11 carried on legs 12, and provided with a cooling pipe 13 extending around the edges thereof. The ends of the re ceptacle are formed by segmental plates 14. The receptacle is composed of any suitable material, e.g., copper. Within the receptacle I provide a liner 15' including a trough-shaped body 16 and esgmental ends 17 of a refractory oxide such as alumina. The oxide of beryllium or thorium could be used in place of alumina.

A semi-cylindrical receptacle 13 having end walls 18a is seated in liner 15. Receptacle 18 has a trough-shaped body and segmental ends and is formed of sheet refractory metal such as molybdenum. Boron, tungsten, tantalum or colurnbium could be used instead of molybdenum. A second liner 19 similar to liner 15 is disposed in receptacle 18 and a third receptacle 20 similar to that shown at 18 is seated within liner 19. The edges of receptacle 20 however are spaced below the edges of liner 19.

3,172,549 Fatented Mar. 9;, 1965 The receptacle Ztl contains a block 21 of a refractory metal such as zirconium extending to a level slightly above its edges. When the exposed surface of the zirconium block 21 is heated above the fusion point as the target of electron bombardment, the block acts as a thermal reservoir and aluminum fed over the edge of the crucible is first melted, falls in drops into the molten zirconium'and immediately flashed into vapor.

The crucible constructed as described herein is characterized by a low heat loss from the heated block of zirconium 21 to the cooling pipe 13. At the same time, there is a minimum exposure of the alumina lining 19 to the zirconium block, and the molybdenum receptacle Zll is shielded from contact by the aluminum. The narrow peripheral strip of alumina which is exposed to both the molten aluminum and molten zirconium reacts very slowly and only small evidences of attack are visible after as much as 40 hours of operation The attack is considerably less than if the alumina is in contact separately with either molten zirconium or molten alumi num thus suggesting a favorable shift of reaction-rate equilibria with both metals present. Outer receptacles 18 and 11 together with liner 16 contribute rigidity to the structure and increase the length of the heat-conducting path. Thus liner 19, even though it may crack and check after numerous cycles of heating and cooling, is confined and supported so that continued service may be obtained.

Although I have disclosed herein the preferred embodiment of my invention, l intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

1. A crucible adapted to be heated by electron bombardment comprising a metal receptacle, a cooling-fluid pipe in heat-exchange relation therewith, a lining of refractory oxide in said receptacle, and an inner receptacle of refractory metal within said lining.

2. Acrucible as defined in claim 1, characterized by the edges of said inner receptacle being spaced below the edges of said lining.

3. A crucible as defined in claim 2, characterized by a thermal reservoir comprising a mass of refractory metal substantially filling said inner receptacle and extending to a level above the edges thereof.

4. A crucible as defined in claim 1, characterized by said lining being composed of alumina and said inner receptacle of molybdenum.

References Cited in the file of this patent UNITED STATES PATENTS 1,200,889 Scholes Oct. 10, 1916 1,249,636 Keyes Dec. 11, 1917 1,429,909 Unger Sept. 19, 1922 1,475,650 Osborne Nov. 27, 1923 1,675,119 Marden June 26, 1928 3,046,936 Simons July 3'1, 1962 3,079,451 Pagonis Feb. 26, 1963 FOREIGN PATENTS 21,212 Great Britain 1890 

1. A CRUCIBLE ADAPTED TO BE HEATED BY ELECTRON BOMBARDMENT COMPRISING A METAL RECEPTACLE, A COOLING-FLUID PIPE IN HEAT-EXCHANGE RELATION THEREWITH, A LINING OF REFRACTORY OXIDE IN SAID RECEPTACLE, AND AN INNER RECEPTACLE OF REFRACTORY METAL WITHIN SAID LINING. 